Titanium dioxide pigment grind dispersion and paint

ABSTRACT

A pigment grind dispersion contains non-adsorbed titanium dioxide particles dispersed in an aqueous emulsion containing a mixture of (a) water-insoluble film-forming first polymer particles that adsorb to titanium dioxide particles, the first polymer particle amount in the emulsion being less than the saturation level of adsorption when another polymer is not present, (b) water-insoluble film-forming second polymer particles that do not by themselves form composite particles with titanium dioxide particles, the second polymer particle amount in the emulsion being sufficient to inhibit or interfere with adsorption of the first polymer particles to titanium dioxide particles, and (c) extender particles. The pigment grind dispersion has a titanium dioxide pigment volume concentration of about 25 to about 50 and a titania composite ratio of about 32 to about 60.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/391,322 filed Oct. 8, 2014, which is in turn a national stage filingunder 35 U.S.C. §371 of International Application No. PCT/US2013/037574filed Apr. 22, 2013, which claims priority under 35 U.S.C. §119 to U.S.Provisional Application Nos. 61/789,784 filed Mar. 15, 2013 and61/636,552 filed Apr. 20, 2012, the disclosures of all of which areincorporated herein by reference.

FIELD

This invention relates to pigmented paints and other coatingcompositions.

BACKGROUND

Titanium dioxide is a widely-used but increasingly expensive pigment inpaints and other coating compositions. In many paint formulationstitanium dioxide represents the single most expensive raw material. Anumber of techniques and ingredients have been suggested for reducingthe amount of titanium dioxide in coating composition formulations whilestill providing acceptable light scattering or opacity. One suchingredient is EVOQUE™ Pre-Composite Polymer supplied by Dow ChemicalCompany. EVOQUE products are presently available in four grades (EVOQUE1140, EVOQUE 1180, EXP-4340 and EXP-4463) that are said to havediffering degrees of reactivity towards titanium dioxide. According toits supplier, EVOQUE pre-composite polymer “combines with TiO₂ to form apolymer-pigment composite which improves both the wet and dry hidingefficiency of the pigment.”

Also according to its supplier, “A minimum level of EVOQUE Pre-CompositePolymer is required to fully cover the surface of TiO₂ in order toimprove hiding efficiency and allow for developing stable formulations.”The recited minimum level is sometimes called the “saturation level” or“saturation level of adsorption” (defined below). The saturation levelwill depend on the pigment volume concentration (PVC, defined below),with lesser polymer addition levels being needed to reach the saturationlevel of adsorption at low PVC and greater polymer addition levels beingneeded to reach the saturation level of adsorption at high PVC.

Some patents describing composite pigment particle-forming polymers thatare believed to be like the polymer present in EVOQUE Pre-CompositePolymer say that other copolymers may be present during formation of thecomposite particle, so long as such other copolymers do not inhibit orsubstantially interfere with adsorption of the polymer particle to thepigment particle.

The currently recommended method for making latex paints using EVOQUEPre-Composite Polymer is carried out by dispersing titanium dioxide intoa mixture of EVOQUE Pre-Composite Polymer, water and defoamer to form acomposite, and then combining the composite with the remaining paintingredients including an acrylic latex paint binder in order to form afinished paint formulation. In this method, the acrylic latex paintbinder is not combined with the composite until after the composite hasbeen formed. The resulting paint or other coating composition may attaina given degree of pigment hiding at a somewhat reduced titanium dioxidepigment level, or may attain a somewhat increased degree of pigmenthiding at a given titanium dioxide pigment level. However, the potentialsavings in titanium dioxide raw material costs and the potentialbenefits in pigment hiding efficiency are offset by the EVOQUE productcost.

From the foregoing, it will be appreciated that what remains needed inthe art are improved titanium dioxide-containing coating compositionshaving even lower raw material cost, even greater pigment hidingefficiency, or both lower cost and greater efficiency. Such compositionsand components and methods for their manufacture are disclosed andclaimed herein.

SUMMARY OF THE INVENTION

We have found that paints and other coating compositions havingexcellent opacity and hiding power at low usage levels of both titaniumdioxide and composite pigment particle-forming polymer may be obtainedby disregarding the above-mentioned supplier's requirements andinstructions. Without intending to be bound by theory, we believe thattitanium dioxide may be more efficiently used in a coating compositioncontaining a composite pigment particle-forming polymer if duringcomposite formation, a waterborne emulsion polymer that does not formsuch a composite is present in an amount sufficient to inhibit (forexample, slow down) or otherwise interfere with adsorption of thecomposite-forming polymer particles to the titanium dioxide particles.This can if desired also enable use of less than a saturation level ofthe composite-forming polymer while still providing composite particlesthat efficiently employ titanium dioxide. By using a latex paint binderor other low-cost waterborne emulsion polymer as the interferingpolymer, an overall cost reduction can be achieved together withequivalent or even improved hiding and other paint properties.

The present invention provides, in one aspect, a method for making apigment grind dispersion of titanium dioxide pigment-polymer compositeparticles, which method comprises:

-   -   (a) mixing titanium dioxide particles with an aqueous emulsion        containing:        -   (i) water-insoluble film-forming first polymer particles            that adsorb to the titanium dioxide particles, the first            polymer particle amount in the emulsion being less than the            saturation level of adsorption when another polymer is not            present, and        -   (ii) water-insoluble film-forming second polymer particles            that do not by themselves form composite particles with the            titanium dioxide particles, the second polymer particle            amount in the emulsion being sufficient to inhibit or            interfere with adsorption of the first polymer particles to            the titanium dioxide particles;        -   wherein the pigment grind dispersion has a titanium dioxide            pigment volume concentration of about 25 to about 50 and a            titania composite ratio (TCR, defined below) of about 32 to            about 60; and    -   (b) forming titanium dioxide pigment-polymer composite particles        that provide improved coating composition opacity compared to a        coating composition that does not contain such first polymer        particles.

The present invention provides, in another aspect, a pigment grinddispersion comprising non-adsorbed titanium dioxide particles dispersedin a circulating aqueous emulsion containing a mixture of:

-   -   (a) water-insoluble film-forming first polymer particles that        adsorb to the titanium dioxide particles, the first polymer        particle amount in the emulsion being less than the saturation        level of adsorption when another polymer is not present, and    -   (b) water-insoluble film-forming second polymer particles that        do not by themselves form composite particles with the titanium        dioxide particles, the second polymer particle amount in the        emulsion being sufficient to inhibit or interfere with        adsorption by the first polymer particles to the titanium        dioxide particles,    -   wherein the pigment grind dispersion has a titanium dioxide        pigment volume concentration of about 25 to about 50 and a        titania composite ratio of about 32 to about 60.

The present invention provides, in yet another aspect, a pigment grinddispersion consisting essentially of an aqueous emulsion containing:

-   -   (a) titanium dioxide pigment-polymer composite particles having        water-insoluble film-forming first polymer particles adsorbed to        the titanium dioxide particles, the first polymer particle        amount in the emulsion being less than the saturation level of        adsorption when another polymer is not present, and the        composite particles providing improved coating composition        opacity compared to a coating composition that does not contain        such first polymer particles,    -   (b) water-insoluble film-forming second polymer particles that        do not by themselves form composite particles with the titanium        dioxide particles, the second polymer particle amount in the        emulsion being sufficient to inhibit or interfere with such        adsorption by the first polymer particles to the titanium        dioxide particles, the pigment grind dispersion having a        titanium dioxide pigment volume concentration of about 25 to        about 50 and a titania composite ratio of about 32 to about 60,        and    -   (c) optionally one or more extender particles, dispersing agents        or defoamers.

The present invention provides, in a further aspect, a coatingcomposition containing (i) the above-described pigment grind dispersion,(ii) one or more opacifiers, rheology modifiers, coalescents, wettingagents or waxes, and (iii) optional additional water-insolublefilm-forming emulsion polymer particles that do not adsorb to thetitanium dioxide particles.

The disclosed methods, pigment grind dispersions and coatingcompositions can provide dried coatings having excellent opacity andhiding power at reduced titanium dioxide or composite-forming polymerusage levels. The methods and pigment grind dispersions appear to haveparticular value for making semigloss, gloss, high hiding or superhiding paints and other coating compositions.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing viscosity for a series of compositeparticle-containing pigment grind dispersions prepared according to themanufacturer's recommendation or prepared according to the presentinvention, and measured one hour after composite formation;

FIG. 2 is a graph showing viscosity for a series of compositeparticle-containing pigment grind dispersions prepared according to themanufacturer's recommendation or prepared according to the presentinvention, and measured one hour and 24 hours after composite formation;and

FIG. 3 is a graph showing percent solids as grit for a series ofcomposite particle-containing pigment grind dispersions preparedaccording to the manufacturer's recommendation or prepared according tothe present invention, and measured five days after composite formation.

Like reference symbols in the various figures of the drawing indicatelike elements. The elements in the drawing are not to scale.

DETAILED DESCRIPTION

The recitation of a numerical range using endpoints includes all numberssubsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, 5, etc.).

The terms “a,” “an,” “the,” “at least one,” and “one or more” are usedinterchangeably. Thus, for example, a coating composition that contains“an” additive means that the coating composition includes “one or more”additives.

The terms “adsorb” and “adsorption” when used with respect to titaniumdioxide particles and polymer particles in a fluid medium means that thetitanium dioxide and polymer particles when allowed to equilibrate inthe fluid medium and observed using electron microscopy appear to haveformed stable composite particles in which a sufficient number oftitanium dioxide particles contact a sufficient number of polymerparticles so as to provide an improvement in titanium dioxide particlespacing and contrast ratio in a dried coating composition containingsuch composite particles. If observed using scanning electronmicroscopy, the fluid medium may be evaporated away and the samplesubjected to conventional plating and polishing steps prior toobservation. If observed using transmission electron microscopy, thefluid medium may be drawn down to a thin film and frozen prior toobservation. The observed adsorption may arise due to physisorption,chemisorption, electrostatic attraction or by other means.

The term “architectural paint” means a coating composition for use oninterior or exterior building components, and includes both paints andstains.

The term “binder” means a film-forming natural or synthetic polymersuitable for use in paints and other coating composition.

The term “circulating” when used with respect to a composition meansthat the composition is a fluid that may or may not contain dispersedsolid particles and which is undergoing stirring, agitation or othershear forces sufficient to mix components in the composition.

The term “contrast ratio” means a value determined by casting a 51 μm (2mil) dry thickness coating film over the white and black portions of aLeneta Co. Form 3B opacity drawdown chart (from BYK-Gardner USA),measuring L* as defined in the ASTM International Standards on Color andAppearance Measurement: 8th Edition, and dividing the L* value measuredover the black portion by the L* value measured over the white portion.

The terms “titania composite ratio” or “TCR” when used with respect to apigment grind dispersion, paint or other coating composition mean thetotal percentage of the dried solids volume, excluding extender pigmentsand opaque polymers, occupied by titanium dioxide particles in suchdried solids.

The term “film-forming” when used in reference to a water-insolubleparticulate polymer means that an aqueous dispersion of the polymerparticles can be formed, coated in a thin wet layer (e.g., of about 25μm thickness) on a suitable support, and dried or otherwise hardened(optionally with the aid of a suitable coalescent) to form asubstantially continuous coating over the support.

The term “fluid” when used in reference to a substance means that thesubstance is a liquid that may or may not contain dispersed solidparticles and which has a loss modulus (G″) greater than its storagemodulus (G′) and a loss tangent (tan 6) greater than 1.

The term “low VOC” when used with respect to paints and other coatingcomposition means that the coating composition contains less than about5 wt. percent volatile organic compounds, preferably less than about 3wt. % volatile organic compounds, more preferably less than about 1 wt.% volatile organic compounds and most preferably less than about 0.5 wt.% volatile organic compounds based upon the total coating compositionweight.

The term “opaque” when used with respect to paints and other coatingcomposition means that a dry film of the coating composition has acontrast ratio greater than 95% at a 51 μm (2 mil) dry film thickness.

The term “paint” means a coating composition including pigment and afilm-forming binder which when applied to form a thin (e.g., 100 μm) wetthickness coating film on a freshly-sanded smooth wood surface, will dryto form a continuous film over the surface, and includes non-penetratingor other stains that will dry to form such a continuous film.

The term “pigment” means an inorganic particulate material havinglight-reflective characteristics and a surface energy and particle sizesuitable for use in paints and other coating compositions.

The terms “pigment volume concentration” or “PVC” when used with respectto a pigment grind dispersion, paint or other coating composition meanthe total percentage of dried solids volume, including extender pigmentsand opaque polymers, occupied by a recited pigment species (or if nopigment species is recited, then by all pigment species) in such driedsolids.

The terms “polymer” and “polymeric” include polymers as well ascopolymers of two or more monomers.

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the invention.

The term “primer” refers to a coating composition that is applied in oneor more layers to a bare substrate and which if left uncoated without atopcoat would not be capable of withstanding extended outdoor exposure(e.g., exposure equivalent to one year of vertical south-facing Floridasunlight) without visually objectionable deterioration.

The terms “saturation level” and “saturation level of adsorption” whenused with respect to titanium dioxide particles and polymer particlesthat adsorb to the titanium dioxide particles in a fluid medium mean apolymer addition level at which the amount of polymer adsorbed per unitof titanium dioxide particles plateaus.

The term “solvent-borne” when used with respect to paints or othercoating compositions means that the major liquid vehicle or carrier forsuch coating composition is a nonaqueous solvent or mixture ofnonaqueous solvents.

When used with respect to a component which may be found in a paint orother coating composition, the term “substantially free of” meanscontaining less than about 1 weight percent of the component based onthe coating composition weight.

The term “topcoat” refers to a coating composition which when dried orotherwise hardened provides a decorative or protective outermost finishlayer on a coated substrate. By way of further explanation, suchtopcoats may be applied in one or more layers and may be applied to bareor primer-coated substrates.

The term “water-borne” when used with respect to paints and othercoating compositions means that the major liquid vehicle or carrier forsuch coating composition is water.

The term “water-insoluble” when used with respect to a polymer meansthat particles of the polymer may be mixed (optionally with the aid of asuitable dispersant) into water to form a particulate polymerdispersion.

The disclosed titanium dioxide particles provide light scattering siteswithin a dried film of the disclosed coating compositions, and imparthiding or opacity to the dried film. Representative titanium dioxideparticles can have a variety of forms, including rutile, anatase andBrookite titanium dioxide. Blends, for example of rutile and anatasetitanium dioxide, may also be employed, as well as blends of titaniumdioxide together with pigments other than titanium dioxide.Representative lists of such other pigments may be found in U.S. Pat.No. 5,509,960 (Simpson et al.) and U.S. Pat. No. 7,179,531 B2 (Brown etal.), and in Published U.S. Patent Application No. US 2011/0290152 A1(Gebhard et al. '152). The titanium dioxide particles may have a varietyof shapes and sizes but desirably will scatter photons havingwavelengths in the spectral region from 300 nm to 750 nm and especiallyin the visible spectral region from 380 nm to 700 nm. Suitable shapesfor the titanium dioxide particles include spherical shapes, such as aregular sphere, an oblate sphere, a prolate sphere, and an irregularsphere; cubic shapes such as a regular cube and a rhombus; plate-likeshapes including a flat plate, a concave plate, and a convex plate; andirregular shapes. Particles having spherical shapes desirably haveaverage diameters of about 10 nm to about 1,000 nm, e.g., about 100 nmto about 500 nm, about 200 nm to about 300 nm, or about 230 nm.Particles having non-spherical shapes desirably have a maximum diameterof up to about 1 micrometer, e.g., up to about 500 nm or up to about 300nm. The titanium dioxide particles may include one or more coatings,e.g., of silica, alumina, zirconia or combinations thereof such as asilica coating and an alumina coating. Exemplary commercially availabletitanium dioxide particles include those made by the chloride processand those made by the sulfide process, and those made in slurry or dryforms, e.g., KRONOS™ 1071, 2020, 2044, 2090, 2101, 2102, 2131, 2160,2210, 2310, 4102, 4310 and 4311 from Kronos, Inc., TIONA™ 595 and 596ifrom Millennium Specialty Chemicals Inc. TIPURE™ TS-6200, R-706, R-741,R-746, R-900, R-902+, R-931 and R-960 from E. I. duPont de Nemours andCompany, TRONOX™ CR-813, CR-813S, CR-826, CR-826S, CR-828, CR-834 andCR-880 from Tronox Corporation, and products from other suppliersincluding Bluestar New Chemical Materials Co., Ltd., Hebei ChuanghuiChemicals Co., Ltd., Henan Billions Chemicals Co., Ltd., Ishihara SangyoKaisha, Ltd., Nanjing Hengsiman Chemical Co., Ltd., Pangang TitaniumIndustry Co., Ltd., Qingdao Gracecorp Co., Ltd., Sakai Chemical IndustryCo., Ltd., Shanghai Yuejiang Titanium Chemical Manufacturer Co., Ltd.,Shijiazhuang Kelichuangxin Chemicals Co., Ltd. and Xuzhou ZhonglianChemical Technology Co., Ltd. and mixtures thereof.

A variety of water-insoluble film-forming first polymer particles (the“first polymer”) that adsorb to titanium dioxide particles may beemployed in the disclosed pigment grind dispersions and the disclosedcoating compositions. Exemplary first polymers are described in theabove-mentioned Simpson et al. and Brown et al. patents as well as inU.S. Pat. No. 5,385,960 (Emmons et al. '960), U.S. Pat. No. 6,080,802(Emmons et al. '802), U.S. Pat. No. 6,576,051 B2 (Bardman et al. '051),U.S. Pat. No. 6,881,782 B2 (Crater et al.), U.S. Pat. No. 7,081,488 B2(Bardman et al. '488), U.S. Pat. No. 7,265,166 B2 (Gebhard et al. '166)and U.S. Pat. No. 8,318,848 B2 (Finegan et al.), in European PatentApplication No. EP 0 700 976 A2 (Tioxide Group Services Limited) and inInternational Application No. WO 93/11181 (Emmons et al. '181). Thefirst polymers typically are waterborne addition polymers formed by theaqueous emulsion polymerization of at least one ethylenicallyunsaturated monomer containing a pendant group capable of facilitatingadsorption of the first polymer particles to titanium dioxide particles,and optionally one or more other ethylenically unsaturated monomers.Exemplary such pendant groups include phosphorus groups (e.g.,dihydrogen phosphate groups), acetoacetoxy groups, 1,3-dicarbonylgroups, aldehyde groups, acid groups, amine groups, epoxy groups,isocyanate groups, thiorane groups, isothiocyanate groups, alcoholgroups, carbodiimides groups, aziridine groups, haloalkane groups, andhalophenyl groups. In place of or in addition to the at least oneethylenically unsaturated monomer containing such a pendant group, thefirst polymer may be formed from a reaction mixture containing one ormore ethylenically unsaturated monomers containing a select pendantgroup capable of reacting with a coupling agent that will provide agroup capable of adsorbing the first polymer particle to a titaniumdioxide particle, followed by reaction of the resulting first polymerparticles with such a coupling agent. Exemplary select pendant groupsand coupling agents are described in, e.g., the above-mentioned Bardmanet al. '488 and Brown et al. patents. The first polymer particles may besingle stage or multistage polymers. Exemplary multistage polymers aredescribed in, e.g., the above-mentioned Emmons et al. '960, Emmons etal. '802, Bardman et al. '051, Bardman et al. '488, Brown et al. andFinnegan et al. patents. The glass transition temperature (Tg) of thefirst polymer or the Tg of each stage in a multistage first polymer maybe adjusted to obtain desired properties. For example, a first polymeror first polymer stage having a higher Tg (for example, a Tg of about 30to about 230° C.) may be employed to adjust finished film propertiessuch as film hardness or scrub resistance. A first polymer or firstpolymer stage having a lower Tg (for example, a Tg of about −65 to about30° C.) may be employed to adjust film formation properties such as theminimum film-forming temperature (MFFT), or to make the first polymerself-coalescing without requiring a coalescent. The first polymerparticles may include vesicles or other voids, or may be free of voids.Exemplary commercially available first polymers include EVOQUE 1140,EVOQUE 1180, EXP-4340 and EXP-4463 pre-composite polymer from DowChemical Company, FASTRACK HE-2706 high efficiency binder from DowChemical Company and mixtures thereof.

The disclosed pigment grind dispersions may employ a variety ofwater-insoluble film-forming second polymer particles (the “secondpolymer”) that do not by themselves form composite particles with (forexample, do not adsorb to) the titanium dioxide particles. Exemplarysecond polymers typically are waterborne addition polymers formed by theaqueous emulsion polymerization of one or more ethylenically unsaturatedmonomers that do not contain pendant groups sufficient to causeinterfering adsorption of the second polymer particles to titaniumdioxide particles. Exemplary second polymers include acrylic emulsions,ethylene vinyl acetate emulsions, polybutadiene emulsions,polyvinylidene emulsions, styrene acrylic emulsions, vinyl acrylicemulsions and vinyl acetate-vinyl versatate emulsions and mixturesthereof, with latex emulsions (e.g., acrylic latex emulsions) beingpreferred. The second polymer emulsions normally contain at least thesecond polymeric particles, water, and one or more emulsifiers. Thesecond polymer particles may include one or more functional groupscapable of reacting with an external crosslinker, and such externalcrosslinker may also be a part of the disclosed coating compositions.For example, the second polymer particles may includehydroxyl-functional groups capable of reacting with an amino resin orpolyisocyanate crosslinker. Exemplary such amino resins includewaterborne coating-compatible melamine, urea and glycoluril crosslinkersavailable from suppliers such as Cytec Industries Inc., including CYMEL™328 and CYMEL 383 aminoplast resins. Exemplary such polyisocyanatecrosslinkers include waterborne coating-compatible polyisocyanatecrosslinkers available from suppliers such as Bayer MaterialScience,including BAYHYDUR™ 304 and BAYHYDUR 3100 polyisocyanates. The secondpolymer particles may also include functional groups capable of reactingwith a waterborne coating-compatible polyepoxide crosslinker, orepoxy-functional groups capable of reacting with a waterbornecoating-compatible epoxy curative. Exemplary such epoxy curativesinclude ANQUAMINE™ 721 water-reducible epoxy curative from Air Productsand Chemicals, Inc. and BECKOPDX™ EH 2179W/65WA water-reducible epoxycurative from Cytec Industries, Inc. The second polymer particles mayalso or instead include one or more functional groups capable ofundergoing an internal crosslinking reaction (viz., a so-calledself-crosslinking polymer), or may harden without requiring acrosslinking or other curing reaction for dry film formation to takeplace shortly after application. In some embodiments it will bedesirable to employ a softer second polymer that does not require avolatile coalescent for film formation, and to employ an internal orexternal crosslinking agent to promote film formation. Exemplary secondpolymers may be prepared as described for example in U.S. Pat. No.8,293,361 B2 (Killilea et al.) or obtained from a variety of commercialsources. Exemplary commercially available second polymers includeALBERDINGK AC 2514, ALBERDINGK AC 25142, ALBERDINGK AC 2518, ALBERDINGKAC 2523, ALBERDINGK AC 2524, ALBERDINGK AC 2537, ALBERDINGK AC 25381,ALBERDINGK AC 2544, ALBERDINGK AC 2546, ALBERDINGK MAC 24, andALBERDINGK MAC 34 emulsions from Alberdingk Boley, Inc.; AQUAMAC 720emulsion from Hexion Specialty Chemicals; EPS 2538 acrylic latex, EPS2540 styrene acrylic latex, EPS 2771 acrylic emulsion and EPS 2725acrylic latex emulsions from EPS Corp.; RESYN™ 7305 vinyl acrylicemulsion from Celanese Emulsion Polymers; RHOPLEX™ 3131-LO, RHOPLEX™AC-1020, RHOPLEX E-693, RHOPLEX E-940, RHOPLEX E-1011, RHOPLEX E-2780,RHOPLEX HG-95P, RHOPLEX HG-700, RHOPLEX HG-706, RHOPLEX PR-33, RHOPLEXTR-934HS, RHOPLEX TR-3349, RHOPLEX VSR-1050 and RHOPLEX VSR-2015 acrylicemulsions from Rohm and Haas Co.; RHOSHIELD™ 636, RHOSHIELD 3188 andRHOSHIELD 3275 emulsions from Rohm and Haas Co.; JONCRYL™ 538, JONCRYL1552, JONCRYL 1972, JONCRYL 1980, JONCRYL 1982, JONCRYL 1984, JONCRYL1987 and JONCRYL 8383 acrylic emulsions from BASF Resins; NEOCRYL™A-1127, NEOCRYL A-6115, NEOCRYL XK-12, NEOCRYL XK-90, NEOCRYL XK-98 andNEOCRYL XK-220 acrylic latex polymers from DSM NeoResins, Inc., andmixtures thereof.

The disclosed pigment grind dispersions contain (and the disclosedmethods may employ) water, which may be tap, deionized, distilled,reverse osmosis or recycled water. Preferably the pigment grinddispersion contains sufficient water to facilitate efficient pigmentgrind mixing (e.g., about 20 to about 80 weight percent water based onthe weight of ingredients in the pigment grind dispersion), and a finalcoating composition made from such a dispersion preferably containssufficient water so that about 20 to about 80 weight percent solids andmore preferably about 35 to about 65 weight percent solids are presentwhen the composition is applied to a substrate.

The ingredient amounts in the disclosed pigment grind dispersions willto some extent depend upon the other ingredients present and may beempirically determined. As an example, the titanium dioxide PVC leveland desired film former binder amounts in the final coating compositionmay be used to estimate initial ingredient amounts in the pigment grinddispersion. In general, higher PVC levels will require larger first andsecond polymer amounts in the pigment grind dispersion. When the firstand second polymers are the only film formers in the final coatingcomposition, then increases in the first polymer amount may be offset bydecreases in the second polymer amount, and vice versa. The firstpolymer particle amount is as noted above less than the saturation levelof adsorption when another polymer is not present. The first polymersaturation level of adsorption may be determined using techniques suchas microscopy or viscosity studies on the pigment grind dispersion toestablish the level at which the amount of first polymer adsorbed perunit of titanium dioxide particles plateaus in the absence of the secondpolymer. A second polymer amount sufficient to inhibit or interfere withadsorption of the first polymer particles to the titanium dioxideparticles may be established by dispersing the titanium dioxideparticles into varying amounts of the second polymer particles, addingan amount (e.g., a saturation level amount or the amount actuallyemployed) of the first polymer particles and noting the second polymerconcentration at which the viscosity increase caused by titanium dioxidepigment-first polymer composite particle formation in the absence of thesecond polymer is reduced or at which its onset is noticeably slowed.

As a further guide, a formulator may determine the amounts of titaniumdioxide particles and second polymer needed to achieve a finished paintor other coating composition with desired PVC and hiding powercharacteristics without using the first polymer. A first polymer amountis then chosen to provide efficient use of titanium dioxide particlesand the desired hiding power at the saturation level and optionally atless than the saturation level. As a general guide for use with anaqueous first polymer emulsion containing about 45 wt. % solids and atitanium dioxide slurry containing about 75 wt. % solids, the firstpolymer may be employed at a wet weight (viz., the weight of adispersion including its solids and vehicle) corresponding to about 50to about 200 percent of the titanium dioxide particle wet weight, withamounts around 50 to 150 percent, 50 to 100 percent or 60 to 80 percentbeing preferred. These amounts may be adjusted as needed for use withfirst polymer emulsions containing other solids levels (for example,solids levels of about 30 to 60 or at about 40 to 50 wt. %) and titaniumdioxide slurries containing other solids levels (for example, solidslevels of about 40 to 85 or about 50 to about 75 wt. %). The secondpolymer amount may be reduced by an amount corresponding to the firstpolymer volume solids, so as to maintain a constant PVC level in thestarting point and adjusted coating compositions. The titanium dioxideamount may for example be sufficient to provide a pigment dispersionhaving a titanium dioxide PVC of at least about 21, at least about 22,at least about 23, at least about 24, at least about 25, at least about26, at least about 27 or at least about 30, and up to about 50, up toabout 45 or up to about 40. The selected titanium dioxide level may forexample also be sufficient to provide a pigment grind dispersion havinga TCR of at least about 33, at least about 35, at least about 37, or atleast about 40, and up to about 60, up to about 50 or up to about 45.Somewhat higher PVC levels may be desirable at lower TCR levels, andsomewhat lower PVC levels may be desirable at higher TCR levels. Thedisclosed method and pigment grind dispersion can provide improvedstorage stability (for example, avoidance of undesirable changes inviscosity, such as rapid viscosity increases), reduced grit (viz., solidparticle) formation, or both improved storage stability and reduced gritformation compared to pigment grind dispersions prepared usingpreviously-recommended methods. Improved storage stability, reduced gritformation or both improved storage stability and reduced grit formationare useful for a variety of reasons including facilitating inventorymanagement, process control and process improvement in large-scalemixing of paints and other coating compositions. The pigment grinddispersion in the finished coating composition formulation preferablywill contain about 27 to about 37 weight percent titanium dioxideparticles, about 18 to about 49 weight percent first polymer particles,and about 55 to about 14 weight percent second polymer particles, basedon the dry weights of these particles compared to the total dry weightof ingredients in the pigment grind dispersion.

The disclosed pigment grind dispersions may include optional ingredientsthat assist with or do not unduly interfere with pigment dispersion,such as extender particles, dispersing agents, defoamers, wetting agentsand mixtures thereof. Exemplary extender particles may for example havean index of refraction similar to that of a dried film of the secondpolymer, and may for example not significantly scatter visible light ormay flatten the dried coating appearance. The extender particle index ofrefraction may for example be less than 1.8 and greater than or equal to1.3. The extender particles may for example be small particles having anaverage particle diameter less than or equal to twice the averageparticle diameter of the titanium dioxide pigment-polymer compositeparticles, or large particles having an average particle diametergreater than twice the average particle diameter of the titanium dioxidepigment-polymer composite pigment particles. Exemplary extenderparticles include calcium carbonate, calcium sulfate, barium sulfate,mica, clay, calcined clay, feldspar, nepheline, syenite, wollastonite,diatomaceous earth, alumina silicates, non-film forming polymerparticles, aluminum oxide, silica, talc, mixtures thereof and othermaterials that will be familiar to persons having ordinary skill in theart.

Exemplary dispersing agents include anionic polyelectrolyte dispersantssuch as maleic acid copolymers, acrylic acid copolymers includingmethacrylic acid copolymers, and carboxylic acids such as tartaric acid,succinic acid, citric acid, itaconic acid, mixtures thereof and othermaterials that will be familiar to persons having ordinary skill in theart.

Exemplary defoamers include silicones, ethylene oxide propylene oxidecopolymers, oils and waxes such as FOAMSTAR™ A-32, FOAMSTAR A-34,FOAMSTAR A-36, FOAMSTAR A-38, FOAMSTAR A-39, FOAMASTER™ 111, FOAMASTER333 and FOAMASTER SA-3 from Cognis, TEGO™ FOAMEX™ 810 from Evonik,mixtures thereof and other materials that will be familiar to personshaving ordinary skill in the art, including products from othersuppliers such as Air Products and Chemicals, Ashland, BASF, BYK-GardnerUSA, Cytec, Rhone Poulenc and Troy Corporation.

The amounts of such optional pigment grind dispersion ingredients willnormally be empirically determined. For example, the pigment grinddispersion may contain from zero to more than 100 weight percentextender pigment based on the weight of titanium dioxide pigment.Depending on the type of dispersing agent, the dispersing agent amountmay for example be about 0.3 to about 5 weight percent based on thetotal pigment weight in the pigment grind dispersion.

Other ingredients that may be included in the pigment grind dispersioninclude cosolvents, wetting agents, surfactants, biocides, and pigmentsother than titanium dioxide. Normally however such other ingredientswill be added during a subsequent stage rather than being added to thepigment grind dispersion.

The disclosed composite particles may be prepared by mixing togetheraqueous emulsions containing the disclosed first and second polymerparticles and if need be adjusting the water level and shear rate toprovide a circulating aqueous emulsion containing a uniform mixture ofthe first and second polymer particles. The disclosed titanium dioxideparticles are desirably next added in dry or preferably in slurry form.The order of mixing may be reversed, that is by adding the circulatingaqueous emulsion containing a uniform mixture of the first and secondpolymer particles to a slurry of the titanium dioxide particles. Themixture of first polymer particles, second polymer particles andtitanium dioxide particles is in any event desirably subjected tofurther mixing or otherwise circulated to allow sufficient time for thefirst polymer particles and titanium dioxide particles to form thedisclosed composite particles. The required time will depend upon avariety of factors including the chosen titanium dioxide particle type,amount and surface treatment or coating if any; the respective types andamounts of first and second polymer particles; the optional dispersanttype and amount; the circulation method and shear rate; and temperature.The time required for attainment of a suitable equilibrium level ofcomposite particle formation may for example be from about 5 minutes upto about 2 hours, with shorter or longer times being necessary ordesirable in some instances. The resulting pigment grind dispersioncontains the disclosed composite particles, and may be combined withadditional ingredients to form a finished coating composition. Thedispersion may instead be stored for an appropriate time period andlater used to make a finished coating composition. Some embodiments ofthe disclosed pigment grind dispersions appear to have better storagestability than composite particle-containing pigment grind dispersionsprepared via conventional methods.

The final coating composition is completed by combining the pigmentgrind dispersion with the remaining coating composition ingredients. Thefinal coating composition thus includes the above-described pigmentgrind dispersion together with one or more additional optionalingredients such as film-forming polymers; opacifying non-film-formingcopolymers; coalescents; cosolvents or plasticizers; thickeners andother rheology modifiers; pigments other than titanium dioxide;surfactants or dispersants (aside from those which already may bepresent in the first or second polymers), additional water, and otheradjuvants. The additional film-forming polymer desirably is theabove-mentioned second polymer but may be other film-forming polymersthat will be familiar to persons having ordinary skill in the art. Theamounts and types of such additional film-forming polymers may varywidely and typically will be empirically selected.

Exemplary opacifying non-film-forming copolymers polymers include thosedescribed in, e.g., U.S. Pat. No. 4,885,320 (Biale), U.S. Pat. No.5,663,213 (Jones et al.) and U.S. Pat. No. 6,646,058 B1 (Koger), and inPublished U.S. Patent Application Nos. US 2009/0162558 A1 (Bardman etal. '558) and US 2010/0166967 A1 (Fasano), as well as commerciallyavailable opacifying non-film-forming copolymers such as OPAQUE™ OP-62,OPAQUE OP-96 and OPAQUE™ ULTRA opaque polymers from Dow ChemicalCompany. When an opacifying non-film-forming copolymer is present, thecoating compositions preferably contain about 2 to about 9 weightpercent opacifying non-film-forming copolymer based on the final coatingcomposition weight.

Coalescents may assist in coalescing a film-forming emulsion polymerinto a continuous film. Exemplary coalescents include benzoates such asalkyl benzoates, monobenzoates and dibenzoates; hexanoates such asOPTIFILM™ 400 tri(ethylene glycol) bis(2-ethylhexanoate) from EastmanChemical Co.; dioctyl maleate; oleic acid propylene glycol esters suchas EDENOL™ EFC-100 from Cognis having the formulaHOCH(CH₃)CH₂OC(O)(CH₂)₇CH═CH(CH₂)₇CH₃); UCAR Filmer IBT, UCAR n-propylpropionate, UCAR n-butyl propionate and UCAR n-pentyl propionate fromDOW Chemical Co.; and TEXANOL™ ester alcohol from Eastman Chemical Co.;materials discussed in U.S. Pat. Nos. 6,762,230 B2, 7,812,079 B2 and8,110,624 B2 (collectively, Brandenburger et al.) and in U.S. Pat. No.8,106,239 B2 (Zhou et al.) and U.S. Pat. No. 8,394,496 B2 (Foster etal.), in U.S. Published Patent Application No. US 2009/0149591 A1 (Yanget al.); mixtures thereof and the like. When a coalescent is present,the coating compositions preferably contain about 0.05 to about 10 orabout 0.05 to about 5 weight percent coalescent based on the finalcoating composition weight.

Cosolvents may assist in mixing or coating the composition; may speedup, retard or otherwise change the time or emissions associated withdrying; may improve wet edge properties or overlap characteristics; mayimprove freeze-thaw protection, or may provide or improve otherfeatures, and generally will not be retained in a film of the dried,cured or otherwise hardened coating composition. A chosen cosolvent maybe hazardous air pollutant solvent (HAPS material) but preferably is anon-HAPS material or is substantially free of HAPS materials. Exemplarycosolvents may for example include glycols (e.g., ethylene glycol anddiethylene glycol), glycol ethers (e.g., DOWANOL™ DPM and ButylCELLOSOLVE™ from Dow Chemical Co.), alcohols (e.g., n-propanol,isopropanol, n-butanol, isobutanol, 2-methyl butanol, isoamyl alcoholand other primary amyl alcohol isomers, n-pentanol, 2-ethylhexanol,4-hydroxy-2,6,8-trimethylnonane and diisobutyl carbinol), esters andester alcohols (e.g., isopropyl acetate; n-butyl acetate; isobutylacetate; n-propyl acetate; primary amyl acetate mixed isomers, and UCAR™Ester EEP from Dow Chemical Co.), ketones (e.g., diisobutyl ketone andECOSOFT™ Solvent IK from Dow Chemical Co.), CARBOWAX™ 300 and CARBOWAX600 polyethylene from Dow Chemical Co., mixtures thereof and the like.When a cosolvent is present, the coating compositions preferably containabout 0.1 to about 10 or about 2 to about 5 weight percent cosolventbased on the final coating composition weight.

Plasticizers may improve cured film flexibility, or may provide orimprove other features, and generally will be retained in a film of thedried, cured or otherwise hardened coating composition. In someformulations a plasticizer may perform functions associated with or maybe identified as a coalescent. Exemplary plasticizers include CITROFLEX™4 citric acid ester from Vertellus Specialties Inc. and PARAPLEX™ G-30,PARAPLEX G-41, PARAPLEX G-60, PARAPLEX RGA-2 and PARAPLEX WP-1plasticizers from Dow Chemical Co. When a plasticizer is present, thecoating compositions preferably contain about 0.1 to about 10 or about 2to about 5 weight percent plasticizer based on the final coatingcomposition weight.

Exemplary thickeners and other rheology modifiers include sedimentationinhibitors, hydrophobic ethoxylated urethane resin (HEUR) thickeners,hydrophobically-modified, alkali-soluble or alkali-swellable emulsion(HASE) thickeners), cellulosic thickeners, polysaccharide thickeners andmixtures thereof. Exemplary commercially-available rheology modifiersinclude NATROSOL™ 250 and the AQUAFLOW™ series from Ashland, ATTAGEL™ 50from BASF Corp., the CELLOSIZE™ series and UCAR POLYPHOBE™ T-900 andT-901 from Dow Chemical Co., BENTONE™ AD and BENTONE EW from ElementisSpecialties, LATTICE™ NTC-61 from FMC Biopolymer and ACRYSOL™ RM-6,ACRYSOL RM-8, ACRYSOL RM-12W and ACRYSOL RM-2020NPR all from Rohm &Haas. When a rheology modifier is present, the coating compositionspreferably contain about 0.1 to about 3 or about 0.5 to about 3 weightpercent rheology modifier based on the final coating composition weight.

Exemplary other pigments include those described in U.S. Pat. No.8,141,599 B2 (Korenkiewicz et al.) and U.S. Patent ApplicationPublication No. US 2012/0004359 A1 (Cavallin et al.). The amounts andtypes of such other pigments may vary widely and typically will beempirically selected to provide a desired coating composition tint.

Exemplary surfactants or dispersants include anionic, amphoteric andnonionic materials. Commercially-available surfactants or dispersantsinclude the TAMOL™ series from Dow Chemical Co., nonyl and octyl phenolethoxylates from Dow Chemical Co. (e.g., TRITON™ X-45, TRITON X-100,TRITON X-114, TRITON X-165, TRITON X-305 and TRITON X-405) and othersuppliers (e.g., the T-DET N series from Harcros Chemicals), alkylphenol ethoxylate (APE) replacements from Dow Chemical Co., ElementisSpecialties, Inc. and others, various members of the SURFYNOL™ seriesfrom Air Products and Chemicals, Inc. (e.g., SURFYNOL 104, SURFYNOL104A, SURFYNOL 104BC, SURFYNOL 104DPM, SURFYNOL 104E, SURFYNOL 104H,SURFYNOL 104PA, SURFYNOL 104PG50, SURFYNOL 104S, SURFYNOL 2502, SURFYNOL420, SURFYNOL 440, SURFYNOL 465, SURFYNOL 485. SURFYNOL 485W, SURFYNOL82, SURFYNOL CT-211, SURFYNOL CT-221, SURFYNOL OP-340, SURFYNOL PSA204,SURFYNOL PSA216, SURFYNOL PSA336, SURFYNOL SE and SURFYNOL SE-F),various fluorocarbon surfactants from 3M, E. I. DuPont de Nemours andCo. and other suppliers, and phosphate esters from Ashland, Rhodia andother suppliers. When a surfactant or dispersant is present, the coatingcompositions preferably contain about 0.1 to about 10 weight percent andmore preferably about 1 to about 3 weight percent surfactant ordispersant based on the total composition weight.

The disclosed coating compositions may contain a variety of otheradjuvants that will be familiar to persons having ordinary skill in theart. Representative adjuvants are described in Koleske et al., Paint andCoatings Industry, April, 2003, pages 12-86. Exemplary adjuvants andcommercial examples of the same include anti-cratering agents; biocides,fungicides, mildewcides and preservatives (e.g., BUSAN™ 1292 fromBuckman Laboratories, Inc., NOPCOCIDE™ N-40D from Cognis, KATHON™ LXfrom Rohm & Haas, and POLYPHASE™ 663, POLYPHASE 678 and POLYPHASE PW-40from Troy Corporation); curing indicators; heat stabilizers; levelingagents; light stabilizers (e.g., hindered amine light stabilizers suchas TINUVIN™ 123-DW and TINUVIN 292 HP from Ciba Specialty Chemicals);optical brighteners; ultraviolet light absorbers (e.g., TINUVIN 234 andTINUVIN 1130 from Ciba Specialty Chemicals); wetting agents (e.g., BYK™346 and BYK 348 from Altana, PENTEX™ 99 from Rhodia and TROYSOL LAC™from Troy corporation); waxes (e.g., AQUACER™ 593 from Altana, HYDROCER™303 from Shamrock Technologies, Inc. and MICHEM™ Emulsion 32535 fromMichelman, Inc.); and the like. The types and amounts of these and otheradjuvants typically will be empirically selected.

The disclosed coating compositions may be packaged in any convenientpackaging suitable for storing a desired quantity of the coatingcomposition without premature gelation, undue separation or otherundesirable degradation during storage. Exemplary packaging containersinclude cans, pails, bottles, drums, totes and tanks. The disclosedcompositions may be factory-applied to substrates such as buildingcomponents at a manufacturing site, or may be supplied to end users andapplied onsite to finished articles, e.g., as paints for use on decks,siding, roofing or other surfaces.

The coating compositions may be applied to a variety of substratesincluding metals (including aluminum, brass, copper, iron, pot metal,steel, tin and zinc), woods (including engineered woods, impregnatedwoods and wood-derived materials), plastics (including thermoplasticsand thermosets), composites, and other materials that will be familiarto persons having ordinary skill in the art.

The coating compositions may be applied using a variety of methods thatwill be familiar to persons having ordinary skill in the art, includingspraying (e.g., air-assisted, airless or electrostatic spraying),brushing, roller coating, flood coating and dipping. The compositionsmay be applied at a variety of wet film thicknesses. Preferably the wetfilm thickness is such as to provide a dry film thickness of about 13 toabout 260 μm (about 0.5 to about 10 mil) and more preferably about 25 toabout 75 μm (about 1 to about 3 mil) for the dried coating. The appliedcoating may be cured by allowing it to air dry or by accelerating curingusing a variety of drying devices (e.g., ovens) that will be familiar topersons having ordinary skill in the art. Preferred heating temperaturesfor curing the coating compositions are about 50° to about 65° C., andmore preferably about 60° to about 65° C., and preferred heating timesare at least three minutes and less than 60 minutes, less than 45minutes, less than 30 minutes, less than 15 minutes, less than 10minutes, less than six minutes or less than five minutes. The heatingtime will tend to decrease with increased temperature, increased airflowor decreased humidity.

The invention is further illustrated in the following non-limitingexamples, in which all parts and percentages are by weight unlessotherwise indicated. In several of the examples, tint strength wasevaluated using both untinted (base paint) and tinted samples. Thetinted samples were prepared by adding 11.1 mL (⅜ fluid ounce) thalogreen colorant to 0.47 L (1 pint) of the base paint and mixing theresulting tinted paint on a paint shaker for 5 minutes to incorporatethe colorant. Tint strength was then determined by casting 0.1 mm (4mil) wet thickness films of the untinted and tinted samples on sealedPENOPAC™ panels (Leneta Co., BYK-Gardner USA), allowing the panels todry under ambient conditions for 30 minutes followed by 30 minutes in a50° C. (122° F.) oven, and evaluating the dried paint film reflectancevalues using a DATACOLOR™ 600 spectrophotometer from Datacolor operatedwith a D65 light source, an 8° angle of reflectance, a large area viewusing the included diffuse specular reflection sphere and a 10°observation angle. The results were reported as the untinted or tintedL* values. Untinted paint samples were also assessed for contrast ratio(hiding power) according to ASTM method D-2805, using dried drawdowns onForm 3B Leneta charts prepared at a 0.1 mm (4 mil) wet film thickness.Viscosity was evaluated using a BROOKFIELD™ Model No. CAP-1000+L highshear ICI cone and plate viscometer with a No. 2 spindle operated at 900rpm and 25° C. (77° F.) and reported in poise (P), or evaluated using aBROOKFIELD Model KU-2 Stormer viscometer with its standard paddle bladeoperated at the fixed machine speed and 25° C. and reported in Krebsunits (KU). Storage stability of pigment grind dispersions was evaluatedusing a TA Instruments Model No. AR2000EX rheometer with atemperature-controlled Peltier plate operated at 25° C. Storagestability of finished coating compositions was evaluated by storing asealed 0.47 L (1 pint) finished paint sample in a 49° C. (120° F.) ovenfor one week, removing the sample and inspecting it to ascertain if anyseparation occurred, and then measuring viscosity using the Stormerviscometer and measuring 60° gloss using a Byk Gardner MICRO-GLOSShandheld gloss meter.

Comparison Example A and Examples 1-3

Pigment grind dispersions were prepared by combining and mixing theingredients listed below in Table 1, and then combining the dispersionswith additional ingredients as indicated to make finished paintformulations. The ingredients in Comparison Example A were combined in amanner like that recommended in a May, 2011 Dow Chemical Co. TechnicalData Sheet entitled “EVOQUE Pre-Composite Polymer Technology TechnicalData”, but with ingredient and mixing adjustments to make a semiglosspaint rather than a flat paint. The ingredients in Examples 1-3 werecombined according to the present invention. A number of adjuvants couldbe freely substituted for ingredients present in minor amounts, so thoseingredients were identified generally rather than specifically. Noseparation was observed following oven aging. The Example 1 formulationcontained about 46.5 wt. % solids and about 36 g/L VOCs. Otherproperties for the Comparison Example A and Example 1-3 formulations areshown below in Table 2.

TABLE 1 Comparison Example A, Example 1, Example 2, Example 3,Ingredient Parts Parts Parts Parts INITIAL MIXTURE (PRE- LETDOWN): Water39.5 39.5 39.5 39.5 First polymer (EVOQUE ™ 1140) 285 285 242 200 Secondpolymer (RHOPLEX ™ 146 183 221 VSR-1050) Defoamer 1 1 1 1 TiO₂ slurry(75 wt. % KRONOS ™ 285 285 285 285 4310) Ratio, first polymer emulsion:TiO₂ 1:1 1:1 0.85:1 0.70:1 slurry Water 25 25 25 25 Stir for 10-20minutes Second polymer (RHOPLEX ™ 146 VSR-1050), added w/stirring GRIND:Water 65 65 65 65 Antisettling agent 2 2 2 2 pH buffer (AMP-95) 2.5 2.52.5 2.5 Coalescent (TEXANOL ™) 3 3 3 3 Cosolvent (ethylene glycol) 5 5 55 Dispersant (TAMOL ™ 1124) 2.5 2.5 2.5 2.5 Defoamer 2 2 2 2 Extenderpigment (IMSIL ™ A-10) 20 20 20 20 Preservative 1.6 1.6 1.6 1.6 Mix inHigh Speed Disperser 20 minutes LETDOWN (ADDED TO THE GRIND): Mildewcide2 2 2 2 Surfactant 1 2 2 2 2 Mix 2 minutes Add to Pre-Letdown Water (torinse grind kettle) 30 30 30 30 HEUR thickener (ACRYSOL ™ 25 25 25 25RM-2020NPR) HASE thickener (ACRYSOL RM- 14 14 14 14 6) HASE thickener(1.9 wt. % UCAR 10.5 10.5 10.5 10.5 POLYPHOBE ™ TR-116) Defoamer 2 2 2 2Opaque polymer (ROPAQUE ™ 65 65 65 65 ULTRA) Surfactant 2 1 1 1 1Wetting agent 2 2 2 2 TOTAL PARTS 1034 1034 1034 1034

TABLE 2 Comparison Example A Example 1 Example 2 Example 3 TintStrength, L* 84.11 84.16 84.02 83.98 Contrast Ratio, 99.03 99.36 99.3599.13 0.1 mm (4 mil) Viscosity, P 1.467 1.579 1.546 1.579 Viscosity, KU96.0 100.0 100.3 99.0 Oven-Aged Viscosity, 103.0 104.2 102.2 KUOven-Aged 60° Gloss 39.2 38.1 38.4 38.9

As shown in Table 2, the Example 1 formulation exhibited better tintedL* and contrast ratio values than the Comparison Example A compositepaint made with EVOQUE pre-composite polymer according to themanufacturer's directions, and a slight reduction in oven-aged 60°gloss. The contrast ratio results were especially promising, andindicate the Example 1 paint should provide very good one coat hidingproperties. They also indicate that the paint formulation could beadjusted (e.g., by reducing the titanium dioxide content, first polymercontent or both) to provide a paint with tinted L* and contrast ratiovalues like those in Comparison Example A but at a reduced raw materialcost. Examples 2 and 3 explored one such adjustment, in which the firstpolymer amount was reduced to 85% or 70% of the amount employed inExample 1, with a corresponding upwards adjustment in the amount of theless expensive second polymer. The first polymer amount in Example 1 wasat approximately the saturation level, whereas the first polymer amountsin Examples 2 and 3 were well below the saturation level. The results inTable 2 show that the tinted L* values were slightly reduced but thatimproved contrast ratio values (compared to the Comparison Example Acontrast ratio) were maintained. For these paint formulations, thecontrast ratio improvement had greater overall significance than theslight decrease in the tinted L* value.

Comparison Example B and Example 4

Using the methods employed for Comparison Example A and Example 1,Comparison Example B was prepared using none of the first polymer, 285parts of the titanium dioxide slurry and 410 parts of the secondpolymer, and Example 4 was prepared using 115 parts of the firstpolymer, 285 parts of the titanium dioxide slurry and 110 parts of thesecond polymer. No separation was observed following oven aging. Otherproperties for the Comparison Example B and Example 4 formulations areshown below in Table 3.

TABLE 3 Comparison Example B Example 4 Tint Strength, L* 82.66 84.15Contrast Ratio, 0.1 mm (4 mil) 98.39 99.18 Viscosity, P 1.171 1.537Viscosity, KU 88.0 100.2 Oven-Aged Viscosity, KU — 103.0 Oven-Aged 60°Gloss 39.2 38.1

Comparison Example C and Examples 5-6

Using the methods employed for Comparison Example A and Example 1,pigment grind dispersions were prepared by combining and mixing theingredients listed below in Table 4, and then combining the dispersionswith additional ingredients as indicated to make finished paintformulations. No separation was observed following oven aging. TheExample 5 and 6 formulations contained about 1.8 g/L VOCs. Otherproperties for the Comparison Example C and Example 5-6 formulations areshown below in Table 5.

TABLE 4 Comparison Example Example C, 5, Example 6, Ingredient PartsParts Parts INITIAL MIXTURE (PRE- LETDOWN): Water 35 35 35 First polymer(EVOQUE 1140) 202 202 202 Second polymer (RHOPLEX 215 108 VSR-1050) TiO₂slurry (75 wt. % KRONOS 269 269 269 4310) Ratio, first polymer emulsion:0.75:1 0.75:1 0.75:1 TiO₂ slurry Water 10 10 10 Defoamer 1 1 1 Stir for10-20 minutes Second polymer (RHOPLEX 215 108 VSR-1050), addedw/stirring GRIND: Water 100 100 100 Antisettling agent 2 2 2 Plasticizer(dioctyl maleate) 2 2 2 Dispersant (TAMOL 731) 4.5 4.5 4.5 Defoamer 0.50.5 0.5 Extender pigment (IMSIL A-10) 22 22 22 Preservative 1.67 1.671.67 Mix in High Speed Disperser 20 minutes LETDOWN (ADDED TO THEGRIND): Mildewcide 2 2 2 Surfactant 1 2 2 2 Mix 2 minutes Add toPre-Letdown Water (to rinse grind kettle) 40 40 40 HEUR thickener 40 4040 (AQUAFLOW ™ NHS-310) HEUR thickener (AQUAFLOW 8 8 8 XLS-525) Defoamer2 2 2 Opaque polymer (ROPAQUE 65 65 65 ULTRA) Wetting agent 1 1 1 TOTALPARTS 1025 1025 1025

TABLE 5 Comparison Example C Example 5 Example 6 Tint Strength, tintedL* 83.52 83.56 83.67 Tint Strength, untinted L* 98.17 98.19 98.22Contrast Ratio, 0.1 mm (4 mil) 98.88 99.06 99.02 Viscosity, P 1.4041.437 1.496 Viscosity, KU 100.2 100.3 100.6 Oven-Aged Viscosity, KU 99.799.8 99.2 Oven-Aged 60° Gloss 42.8 42.9 42.7

As shown in Table 5, the Example 5-6 formulations exhibited excellentproperties including improved contrast ratios.

Example 7

Using the methods of Comparative Example A and Example 1, a series ofcomposite particle dispersions containing varying amounts of the firstpolymer and titanium dioxide were prepared and stored. The dispersionswere evaluated to determine whether their viscosity changed duringstorage. The results are shown in FIG. 1 and FIG. 2, with FIG. 1illustrating a plot of viscosity in poise at a 0.05/s shear rate on thevertical axis vs. the TCR value on the horizontal axis for pigment grinddispersions evaluated one hour after composite formation. Curve A showsthe viscosity of five formulations prepared like Comparative Example A,and Curve B shows the viscosity of five formulations prepared accordingto the present invention and as in Example 1. FIG. 1 shows a steepincrease in viscosity for higher-TCR pigment grind dispersions preparedfrom EVOQUE pre-composite polymer and mixed according to themanufacturer's directions, and little or no increase in viscosity forboth lower and higher TCR pigment grind dispersions prepared accordingto the present invention.

FIG. 2 shows a similar plot of viscosity vs TCR value for the samepigment grind dispersions evaluated at one hour and 24 hours aftercomposite formation. Curves C and D respectively show the viscosities offive formulations prepared like Comparative Example A at one hour and 24hours after composite formation. Curves E and F (which overlay oneanother) respectively show the viscosities of five formulations preparedaccording to the present invention as in Example 1 at one hour and 24hours after composite formation. The results in FIG. 1 and FIG. 2 showthat pigment grind dispersions prepared according to the presentinvention have improved storage stability.

Example 8

Using the ingredients employed in Example 1, several titanium dioxidepigment-polymer composite particle dispersions were prepared and stored.Each composite particle dispersion included sufficient ingredients andadded water to provide 37% non-volatile material by volume (NVV). Twopreparation methods were employed, and were respectively identified asMethod A and Method B. Method A is a method of the invention, and MethodB is the method recommended by the first polymer supplier. In Method A,a letdown containing all water in the formulation and the first andsecond polymers was mixed and then a titanium dioxide slurry was addedto the mixture and mixed for a further 15 minutes. In Method B, aletdown containing an aqueous dispersion of the first polymer was mixed,a titanium dioxide slurry was added to the mixture and mixed for afurther 15 minutes, and the remaining water in the formulation and thesecond polymer were added and mixed for an additional 15 minutes. Theresulting composite particle dispersions were allowed to stand for 5days at room temperature, filtered through a 240 micrometer screen andrinsed with cold water to remove soluble residues. The filtrate wasdried overnight in a 49° C. (120° F.) oven to remove water and thenweighed. The filter medium mass was subtracted from the total mass todetermine the grit content. The amounts of first polymer, second polymerand titanium dioxide in each sample are shown below in Table 6, withboth the total mass of each component (including water in the componentas supplied) and the percent non-volatile materials by mass (NVM) ofeach component being reported. The grit amounts after storage are shownbelow in Table 7, along with the calculated NVV, TCR and PVC values. TCRvalues were determined as:TCR=(Volume Solids TiO₂)/(Volume solids TiO₂+Volume Solids EVOQUE 1140)PVC values were determined as:PVC=(Volume Solids TiO₂)/(Volume solids TiO₂+All Latex Volume Solids)The grit content in each sample as a percent of total non-volatilematerials is also shown graphically in FIG. 3.

TABLE 6 First Second Second Polymer Polymer TiO₂ Polymer (EVOQUE(RHOPLEX (KRONOS (RHOPLEX 1140) VSR-1050) 4310) VSR-1050) Sample Methodgrams NVM grams NVM grams NVM grams NVM 1a A 93.66 43.55 36.29 17.96100.00 75.00 1b B 93.66 43.55 100.00 75.00 36.29 17.96 2a A 93.66 43.558.64 4.28 100.00 75.00 2b B 93.66 43.55 100.00 75.00 8.64 4.28 3a A53.65 24.95 73.73 36.50 100.00 75.00 3b B 53.65 24.95 100.00 75.00 73.7336.50 4a A 53.65 24.95 26.33 13.03 100.00 75.00 4b B 53.65 24.95 100.0075.00 26.33 13.03

TABLE 7 Filterable % Solids Sample Method NVV TCR PVC solids as Grit 1aA 37 32 25.00 0.12 0.09 1b B 37 32 25.00 0.53 0.39 2a A 37 32 30.00 0.280.23 2b B 37 32 30.00 2.37 1.93 3a A 37 45 25.00 0.53 0.39 3b B 37 4525.00 39.37 28.85 4a A 37 45 35.00 50.53 44.72 4b B 37 45 35.00 59.5052.66

The results in Table 7 and FIG. 3 show significant storage stabilityimprovement, manifested by significant grit reduction is during storage,for composite particle dispersions prepared according to Method A ratherthan according to Method B (the method recommended by the first polymersupplier).

Having thus described preferred embodiments of the present invention,those of skill in the art will readily appreciate that the teachingsfound herein may be applied to yet other embodiments within the scope ofthe claims hereto attached. The complete disclosure of all patents,patent documents, and publications are incorporated herein by referenceas if individually incorporated.

We claim:
 1. A pigment grind dispersion comprising non-adsorbed titaniumdioxide particles dispersed in an aqueous emulsion containing a mixtureof: (a) water-insoluble film-forming first polymer particles that adsorbto titanium dioxide particles, the first polymer particle amount in theemulsion being less than the saturation level of adsorption when anotherpolymer is not present, (b) water-insoluble film-forming second polymerparticles that do not by themselves form composite particles withtitanium dioxide particles, the second polymer particle amount in theemulsion being sufficient to inhibit or interfere with adsorption of thefirst polymer particles to titanium dioxide particles, and (c) extenderparticles, wherein the pigment grind dispersion has a titanium dioxidepigment volume concentration of about 25 to about 50 and a titaniacomposite ratio of about 32 to about
 60. 2. A pigment grind dispersionaccording to claim 1, further comprising a dispersing agent.
 3. Apigment grind dispersion according to claim 2, wherein the dispersion iscirculating.
 4. A pigment grind dispersion according to claim 3, furthercomprising a defoamer.
 5. A pigment grind dispersion according to claim1, having a titanium dioxide pigment volume concentration of about 30 toabout
 50. 6. A pigment grind dispersion according to claim 1, having atitania composite ratio of about 32 to about
 50. 7. A pigment grinddispersion according to claim 1, containing about 27 to about 37 weightpercent titanium dioxide particles, about 18 to about 49 weight percentfirst polymer particles, and about 55 to about 14 weight percent secondpolymer particles, based on the dry weights of these particles comparedto the total dry weight of ingredients in the pigment grind dispersion.8. A pigment grind dispersion according to claim 7, containing up toabout 100 weight percent extender particles based on the weight oftitanium dioxide particles.
 9. A pigment grind dispersion according toclaim 1, wherein the first polymer particles include pendant phosphorusgroups, acetoacetoxy groups, 1,3-dicarbonyl groups, aldehyde groups,acid groups, amine groups, epoxy groups, isocyanate groups, thioranegroups, isothiocyanate groups, alcohol groups, carbodiimide groups,aziridine groups, haloalkane groups, or halophenyl groups.
 10. A pigmentgrind dispersion according to claim 1, wherein the first polymerparticles include pendant phosphorus groups.
 11. A pigment grinddispersion according to claim 10, wherein the phosphorus groups includeacid groups.
 12. A pigment grind dispersion according to claim 10,wherein the phosphorus groups include dihydrogen phosphate groups.
 13. Apigment grind dispersion according to claim 1, wherein the first polymerparticles are multistage polymers.
 14. A pigment grind dispersionaccording to claim 1, wherein the first polymer particles are free ofvoids.
 15. A pigment grind dispersion according to claim 1, wherein thesecond polymer particles comprise acrylic, ethylene vinyl acetate,polybutadiene, polyvinylidene, styrene acrylic, vinyl acrylic or vinylacetate-vinyl versatate particles, or a mixture thereof.
 16. A pigmentgrind dispersion according to claim 1, wherein the second polymerparticles are acrylic latex particles.
 17. A coating compositioncomprising a pigment grind dispersion according to claim 1, andadditional water-insoluble film-forming emulsion polymer particles thatdo not adsorb to the titanium dioxide particles.
 18. A coatingcomposition according to claim 17, further comprising one or morepigments other than titanium dioxide.
 19. A coating compositionaccording to claim 17, further comprising one or more coalescents,cosolvents or plasticizers.
 20. A coating composition according to claim17, further comprising one or more rheology modifiers.